class Solution {
  public:
    int m, n;
    int dx[4] = {0, 0, 1, -1};
    int dy[4] = {1, -1, 0, 0};
    int vis[1001][1001] = {0};
    int rotApple(vector<vector<int> >& grid) {
        m = grid.size(), n = grid[0].size();
        queue<pair<int, int>> q;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == 2)
                    q.push({i, j});
            }
        }
        int ret = 0;
        while (q.size()) {
            int sz = q.size();
            ret++;
            while (sz--) {
                auto [a, b] = q.front();
                q.pop();
                for (int i = 0; i < 4; i++) {
                    int x=a + dx[i], y=b + dy[i];
                    if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == 1 && vis[x][y] != 1) {
                        vis[x][y] = 1;
                        q.push({x, y});
                    }
                }
            }
        }
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == 1 && vis[i][j] == 0)
                    return -1;
            }
        }
        return ret - 1;
    }
};